1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device in which a semicondnctor element is mounted on a mounting surface of a mounting section while a portion of the non-mounting surface of the mounting section is molded in a frame-shaped configuration with a molding material.
2. Description of the Related Art
FIG. 10 shows, in a side sectional view, an example of a conventional semiconductor device. Referring to the drawing, the device has a semiconductor element 1 adhered to and mounted on a surface (upper surface, as viewed in FIG. 10) of a mounting section 2 by an adhesive 3. Inner leads 5 are electrically connected with the semiconductor element 1 by wires 4. The semiconductor element 1, the mounting section 2, the adhesive 3, the wires 4, and the inner leads 5 are molded with a molding material 6 into a molded structure. Certain portions of lead members continuing from the inner leads 5 and extending outside of the molding material 6 constitute outer leads 7.
In the conventional semiconductor device having the above construction, the molded structure of the device has a total thickness D, the semiconductor element 1 has a thickness d.sub.1, and the portion of the molding material 6 disposed below, or on the reverse side of the mounting section 2, has a thickness d.sub.2. When the total thickness D of the molded structure is reduced to reduce the entire thickness of the semiconductor device, the thickness d.sub.2 of the reverse portion of the molding-material 6 is reduced correspondingly. In a resin molding process, this portion of the molding material 6 may not thoroughly cover the reverse surface of the mounting section 2, and thus, the encapsulation characteristics of the molding material 6 may be impaired. Although the thickness d.sub.1 of the semiconductor element 1 itself may be reduced, it is not easy to reduce this thickness d.sub.1 without involving disadvantages such as decreased reliability of the semiconductor element 1.
It has been the recent demand from the market that semiconductor devices have high heat radiation characteristics. In order to obtain high heat radiation characteristics it is possible to adopt, for example, a construction in which the mounting section 2 is exposed to the outside of the device.
FIG. 11 shows, in a side sectional view, an example of a conventional semiconductor device constructed to have an exposed portion. As shown in FIG. 11, the entire reverse surface of the mounting section 2 is exposed. As a result, however, stress is concentrated on an edge 2A of the mounting section 2. This is disadvantageous in that the molding material 6 and the mounting section 2 may be separated at the interface therebetween, thereby adversely affectlng the reliability of the semiconductor device.
Thus, the conventional semiconductor devices have the following problems: the molding characteristics of a molding material are impaired at a portion of the material disposed on the reverse side of the mounting section; and a construction in which the mounting portion is partly exposed in order to obtain high heat radiation characteristics adversely affects the reliability of the semiconductor device.